Strain-relief bushing



July 29, 1947. KLUMPP, JR 2,424,758

STRAIN-RELIEF BUSHING Filed June 14, 1945 FIG. 4 FIG. 6

IN VEN TOR.

FERDINAND KL UMPR JR.

Patented July 29, 1947 STRAIN-RELIEF BUSHING Ferdinand Klumpp, Jr.,Union, N. J., assignor to Heyman Manufacturing Company, Kenilworth,

Application June 14, 1945, Serial No. 599,494

9 Claims.

This invention relates to a self-locking strainrelief bushing which isadapted to securely lock an electrical conductor or cable in the bushingand to a plate or support in which the bushing is inserted. It is theprincipal object of my invention to provide a self-locking strain-reliefbushing which can be easily installed in a plate or support but whichwill more positively lock a conductor or cable to the bushing than anyother strain-relief bushing with which I am familiar. At the same timethe bushing is designed to corelate with its mounting plates so that itcannot be turned in the support member thereby preventing any chance ofthe conductor or cable being displaced from its mounting in the supportplate. The improved characteristics of my new strain-relief structurewill be readily appreciated by reference to the annexed drawing whereinthe figures illustrate my new structure on an enlarged scale,approximately three to one, of one form of the device.

In the drawing:

Figure 1 is a plan view of the body member I supporting the conductor orcable.

Figure 2 is a side view of Figure 1.

Figure 3 is a'view of Figure 2 looking from right to left.

Figure 4 is a side elevational view of the gripping block which is usedwith the body portion.

Figure 5 is a top plan view of Figure 4.

Figure 6 is a view of Figure 4 looking from right to left.

Figure 7 is a fragmentary view of the mounting plate showing a preferredtype of hole for receiving the strain-relief device.

Figure 8 is a part sectional and part elevational view of thestrain-relief device in an initial step of gripping a cable orconductor.

Figure 9 is a part sectional and part elevational view showing thestrain-relief device fully installed in the mounting plate with theconductor or cable in locked position.

In the various views wherein like numbers refer to corresponding parts,I is the body portion of the strain-relief device which is made ofstrong insulating material. The body I has a flange 2 which is adaptedto engage one side of a mounting plate or support member 3 having a holell therein with at least one straight side 5, two being shown, to engagecooperative fiat sides 6 on the body I to prevent the body I fromturning in the mounting plate.

The body I has a longitudinal passageway therethrough. This passagewayis divided into two offset sections, 1 and 8 as is best shown in Figures8 and 9. As illustrated, these passageways are rectangular in shape toreceive a twin conductor. Intercepting this passageway is an opening 9that i rectangular in shape. As shown in Figure 1 the opening 9 projectsa slight distance into a portion of the flange 2 for a purpose whichwill be later explained. The opening 9 also has a channel I0 leadinginto said passageway to receive the edge H of a gripping block I? madeof strong insulating material which is adapted to slidably fit in theopening *9. The block l2 has a tapered surface I3 to cooperate with thecorresponding surface [4 on the body I to assist in assembling thestrain-relief device into the mounting plate 3. The block I2 has anarcuately formed groove l5 having an edge l6 which is adapted to comeinto alignment with the inner edge I! of the flange 2 whereby the grooveI5 will be in the same plane with an arcuately formed groove [8 in thebody I and extending at least part way around the body I as indicated bythe dotted line It in Figure 3. These grooves are provided to engage themounting plate 3 when the device is assembled as shown in Figure 9. Theblock l2 has ofiset shoulders l9 and 20 to cooperate with the offsetpassageways I and 8 in the body I. It will be seen that when the deviceis forced into the hole 4 in the mounting plate 3 the cable or conductorC will be forced by the gripping block [2 into a position somewhatsimilar to that shown in this figure. The gripping block l2 has someclearance in the opening 9 so that it will tilt somewhat when a pullingstrain is applied to the conductor C and will further increase its gripon the conductor.

Where, in the claims, I have used the term conductor this is meant toinclude a single insulated conductor or twin conductor it beingunderstood that the passageways I and 8 in the body of the strain-reliefbushing are made to suit the type of conductor which is to be employedwith the bushing.

I have found from many tests that the insulation of the conductor is notinjured by the gripping block of my improved bushing as is the case withmany other types of strain-relief devices. The reason for this is thatthe conductor is given a bend that does not injure the insulation but,as will be readily appreciated, the bend securely positions theconductor in the body of the bushing. To facilitate handling of thebushing prior to and during assembly, the gripping block I2 may be heldin the position approximately as shown in Figure 8 by a thin filmmaterial, or equivalent means, which can be readily broken away by thepressure applied to the block when assembling it into the position shownin Figure 9.

What I claim is:

1. A strain relief bushing of strong insulating material for holding anelectrical conductor in a mounting plate hole, comprising a body portionhaving a flange at one end only to engage a mounting plate on one sidethereof, the bushing having a single transverse opening through its walland extending beyond the central longitudinal axis of the bushing with alongitudinal passageway at each end of the body leading into saidopening, a grip block slidably but non-rotatably fitting in said openingand having a groove on its outer surface so positioned that at least oneside of the groove is in substantially the same plane with the inneredge of the flange, the block having a height such that when it i forcedinto a hole in a mounting plate, it will project well below the axes ofsaid longitudinal passages and will be forced into strong grippingengagement with a conductor which may be inserted through saidpassageways,

2. A strain relief bushing of strong insulating material for holdin anelectrical conductor in a mounting plate hole, comprising a body portionhaving a flange at one end only, with a circular groove next to theflange and arcuately extendin at least part way around the body so as toengage a mounting plate, the bushing having a longitudinal passagewaytherethrough and an opening through the wall of the body into saidpassageway, a grip block having a contour to slidably but non-rotatablyfit said opening and having a groove in arcuate alignment with thepartial groove in the body, the block having a height such that when itis forced into a hole in a mounting plate it will be forced by the wallof the plate hole into strong gripping engagement with a conductor whichmay be inserte through said passageways, the body having at least onefiat surface positioned adjacent the flange and at right angles theretoto engage a cooperating surface in a mountin plate to prevent 1e bodyfrom turning in said plate.

3. A strain relief bushing as set forth in claim 2 further characterizedin that the two parts of the longitudinal passageway, which isintercepted by said grip block opening, are offset whereby the gripblock when in locked position puts a revers locking bend in theconductor.

4. A strain relief bushing of strong insulating material for holding anelectrical conductor in a mounting plate hole, comprising a body portionhaving a flange at one end and a rectangularly shaped transverse openingadjacent said fiange, the bushin having offset conductor passagewayslocated one at each end of the bushing and leading into said opening,one of the side walls of the said opening having a channel therein, agrip block having a form to slidably fit said opening including thechannel, the outer part of said block having a groove therein to fit amounting plate, the body having at least a groove of some arcuate lengthlocated opposite to the groove in the grip block when it is in grippingposition, the height of the block being such that when it is directlyacting on and forced inwardly and held by the wall of the hole in themounting plate it will force a conductor going through the passagewaysinto a locking reverse bend, the body having means to cooperate with amounting plate to prevent the bushing turning in the plate.

5. A strain relief bushing as set forth in claim 4 further characterizedin that the grip block opening extends into the flange and the block hasshoulders of different heights to cooperate with said offset passagewaysand further characterized in that the body and block have tapered endsfor assistin in assembling the bushing in the mounting plate hole.

6. In combination with a mounting plate having a hole therein tonon-rotatably receive a strain relief bushing, a bushing of stronginsulating material to fit said hole, the bushing having a transverseside opening and two longitudinal offset passageways located one at eachend of the bushing and leading into said opening, a grip block of stronginsulating material slidably but preferably tiltably fitting saidopening and adapted, when forced with the bushing into the plate hole,to be moved across said passageways to grip a conductor by bending itand means on the block and body to lock the bushing in the plate hole.

7. The combination with a mounting plate having a hole therein toreceive a strain relief bushing, of a bushing having a body of goodinsulating material to fit said hole with means for preventing rotationof the body in the hole, said body having a transverse opening withlongitudinal passageways located one at each end of the body and leadininto said opening and a block of good insulating material slidablyfitting in said opening and having means cooperative with the body forlocking the bushing to the plate when inserted in the plate hole, theblock when in looking position extending outwardly beyond the body ofthe bushing and being directly engaged by the wall of the plate hole andforced into strong gripping engagement with a conductor going throughthe passageway.

8. The combination of a mounting plate and a strain relief bushing asset forth in claim 7 further characterized in that said passageways areoffset in the body and the block has parts to cooperate therewith so asto put a bend in the conductor within the bushing when installed in saidplate.

9. The combination of a mounting plate having a hole therein to receivea strain relief bushing of suitable insulating material, the bushingbeing composed of two parts to grip an electrical conductor or cableplaced between them, one part having a recess therein while the otherpart is slidable as a whole into the recess toward the longitudinal axisof said one part, said slidable part having a projection for engagingsaid conductor or cable, each part havin a tapered end to assist inentering the parts into said hole, the two parts being directly forcedtoward each other by the wall of the hole so the said projection willforce the conductor or cable downwardly into said recess, both partshaving cooperative arcuate grooves to lock the parts to the mountingplate.

FERDINAND KLUMPP, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Germany Feb, 15, 1937

